A variety of valve devices are in use for controlling the flow of fluids communicating from a supply port to a service port through an actuating member. In a rotary valve it is known to use a circular valve plate rotatable about a central axis having fluid channels on one plane thereof. The valve plate abuts one plane of a valve body having supply ports and service ports spaced apart. The valve plate may be rotated so as to align the fluid channels with the supply ports and service ports presenting an orifice to one plane of the valve body, thereby diverting the flow of fluid from a supply port to a service port. In a rotary valve, usually the fluid channel is kidney-shaped and the supply ports and service ports in the valve body are spaced apart in an annular configuration corresponding to the kidney-shaped sector defined by the fluid channel. As it may be desirable to control the supply of fluid to more than one service port, one valve plate may have a plurality of kidney-shaped fluid channels which may be spaced one from the other about a common axis, either circumferentially an equal radial distance from the centre or concentrically a varying radial distance from the common central axis. A plurality of supply ports and service ports may be spaced concentrically in one plane of the valve body so as to correspond to the plurality of fluid channels carried by the rotatable valve plate. In a rotary valve having a plurality of fluid channels for selectively interconnecting a plurality of ports it is therefore necessary to accurately control the angle of rotation of the valve plate in order to provide intermediate positions of adjustment, thereby directing multiple flow paths.
It has been known to utilize an electric motor to rotate a valve plate in a rotary valve, wherein the rotational torque of the electric motor is proportional to the magnitude of the current supplied to the motor. However, it has not been possible with such torque motors to achieve a predetermined angle of rotation sufficient to control in discrete increments the position of an actuating member, without the use of feedback means to determine the position of the actuating member, that is a "closed loop system".
U.S. Pat. No. 4,339,737 ("Meyers") 1982, teaches an electrically actuated rotor for controlling the flow of fuel in an internal combustion engine. As noted in Meyers, the rotor portion of the structure need not be limited to a valve device utilized in a fuel line of an internal combustion engine, and may be employed as an actuator per say. A rotor is provided which is adapted to rotate within a predetermined sector to normally assume one of two positions. A coil is provided to which current is applied to generate a magnetic field. Circumferentially spaced magnetic pole means are provided in proximity to the coil whereby when current is applied to the coil the rotor assumes a predetermined position of rotary adjustment responsive to the magnetic field generated by the energized coil. When the current is removed from the coil the rotor is biased to normally assume a predetermined position. It will be appreciated that in Meyers only two positions of adjustment are possible and no intermediate position of adjustment are possible.
U.S. Pat. No. 4,345,228 ("Idogaki") relates to an electric motor mechanically linked to an actuating member in a rotary valve. The actuating member is rotatable by means of the electric motor which is operable to produce a torque proportional to the magnitude of the input current supplied to the motor. Idogaki teaches that is is known in the prior art to provide a bipolar electric motor of an angle of rotation of less than about 180 degrees having a return coil spring connected to the shaft of the motor "so that the motor shaft is rotated to a position where balance is attained between the driving torque produced electromagnetically in accordance with the input current and the recovery force exerted to the motor shaft by the return spring". However, in such a structure the angle of rotation attained with a given magnitude of input current is greater when current is decreasing than the angle of rotation attained when current is increasing. Idogaki explains this relative hysteresis when current is increasing in prior art devices as arising from "the friction between the motor shaft and bearing, the friction between the turns of the coil spring and so forth". Idogaki therefore provides an electric motor suitable for imparting an angle of rotation of less than 180 degrees having a hollow shaft and tortion bar housed coaxially in the shaft. One end of the tortion bar is fixed to the shaft, the other end to the valve housing. The tortion bar thereby acts against the rotational driving torque of the electric motor. As best as may be determined from the disclosure in Idogaki, the tortion bar stores energy in response to one direction of rotation when the input current is decreasing and releases such energy in response to the direction of rotation when the input current is increasing, thereby reducing the relative hysteresis of the rotational characteristics of the motor when current is increasing. It will be appreciated by those skilled in the art that while Idogaki thereby teaches a structure where the amount of torque applied to the shaft is equalized for two opposite directions of rotation so as to overcome frictional imbalances and hysteresis associated with the electro-magnetic induction, there is still not disclosed a means to control the angle of rotation achieved in discrete increments.
U.S. Pat. No. 4,364,111 ("Jocz") relates to a conventional alternating current motor having its output shaft mechanically linked to an actuating member in a valve. The actuating member is movable by means of rotation of the output shaft of the motor between a first position in which the valve is closed and a second position in which the valve is open. The actuation of the motor is controlled by means of an electronic circuit including a microprocessor comprising control logic, and input signals from optical transducers optically coupled to either the output shaft of the motor or the valve actuating member. The optical transducers generate an electrical signal representative of the direction and degrees of angular rotation of the output shaft. The control logic compares values corresponding to the position of the valve actuator when the valve is fully open and when the valve is fully closed to the value of the input signals from the optical transducers, to generate a value indicative of the current position of the valve actuating member. Means are disclosed to control the magnitude of the input current to the AC motor so as to increase or decrease the rotational torque produced electromagneticallly. An amount of torque approximately 50% greater than the average dynamic torque required to drive the valve actuating member may be applied to overcome the relatively greater frictional lag of the valve when the actuator is in the closed position. It will be appreciated by those skilled in the art that "Jocz" discloses sensor feedback means to control the magnitude of the input current supplied to an AC motor as means to increase or decrease the rotational torque produced electromagnetically. It will further be appreciated by those skilled in the art that "Jocz" has addressed the problem associated with torque motors wherein controlling the magnitude of the current applied to the motor will not determine its stopping position, by providing a "closed loop system" comprising feedback sensors.
The use of "closed loop systems" such as that taught by "Jocz" leads to a problem known to those skilled in the art as oscillation or instability. A feedback sensor can only determine when a valve member has reached a known position and will not prevent a valve member from over shooting that position once the feedback signal causes a control unit to cut off power to the motor. To solve this problem the so called "bang bang system" oscillates the motor back and forth to arrive at a position which is an average of the desired stopping point. The effect of such a system is to cause friction which leads to the valve components wearing out.
Inter-Hydraulik A.G., a Swiss company, markets a digitally controlled modulating valve, comprising a rotary stepping motor for actuating the movement of a linear spool valve. When the valve is powered up the linear spool is automatically driven into a null (.phi.) or home position. A closed loop control system may monitor the movement of the linear spool in relation to the null position and compare same to the control input to the stepper motor. In the event of a loss or interruption of power to the valve however, the known position of the linear spool may be lost. It is therefore an object of this invention to provide an improved rotary valve and components therefore.
Is is a further object of this invention to provide improved means for actuating a valve actuating member in a rotary valve.
It is a further object of this invention to provide improved means for actuating a valve actuating member whereby sensor feedback means for determining the position of the actuating member are not required.
Further and other objects of the invention will be apparent to those skilled in the art from the following summary of the invention and detailed description thereof.